Dry Eye Dx and Tx

Protecting Dry Eyes From Harm

dry eye dx and tx

Protecting Dry Eyes From Harm

BY WILLIAM TOWNSEND, OD, FAAO

The surface of a dry eye is a fragile thing. Alterations in tear film osmolarity, electrolyte composition, surface mucins, microvilli and blink rate render the ocular surface susceptible to insult.

In dry eye syndrome the altered composition of ocular surface cells often demonstrates the extent to which normal cellular architecture has been affected. Marube and Rivas (2003) obtained conjunctival biopsies from Sjögren's Syndrome patients and found progressive stratification, hyperplasia, hypertrophy and cellular flattening of conjunctival cells; they also found a reduction in goblet cell density and mucous layer thickness. These cellular changes render the surface more susceptible to loss of surface-adherent mucins and rapid tear film breakup, ultimately leaving underlying conjunctival and corneal surface cells unprotected.

Watch for Preservatives

In prescribing products for dry eye patients, consider the potential effects a preparation may have on ocular surface tissue. The most common preservative in ophthalmic preparations is benzalkonium chloride (BAK). Göbbels and Spitznas (1992) found use of BAK-preserved artificial tears increased corneal permeability more than no treatment at all. In other words, dry eye patients are better off using no artificial tears than BAK-preserved options.

A study by De Saint et al (1999) showed that conjunctival epithelial cells exposed to BAK in concentrations from 0.1% to 0.0001% exhibited dose-dependent growth arrest and cell death.

But some defend the use of BAK for ophthalmic solutions. Abelson and Fink (2002) found that epithelial cells exposed to commercially available concentrations of BAK did not significantly differ from those exposed to preservative-free eye drops.

Adverse effects of medications can extend beyond simple toxicity; Ozdal et al (2002) showed that many ocular preparations are chemotactic for neutrophils. Several studies have established the undesirable effect of chronic medications such as glaucoma therapy. Long-term topical therapy can increase inflammatory mediators and cause changes in connective tissue. Guenoun et al (2005) evaluated three topical prostaglandin analogs for cytotoxic and apoptotic effects and concluded that inherent toxicity of the analogs was less important than the deleterious effects of preservatives, specifically BAK.

Prescribing for Dry Eyes

We must carefully weigh the benefits of a medication against the potential complications or damage from chronic use when prescribing for dry eye patients. Following are some guidelines: